Tests are known for detecting the presence in blood samples of antibodies to microorganisms including viruses such as AIDS and ATLV/HTLV. The known tests use purified or partially purified inactivated virus or antigens as the basis for an immunoassay procedure, e.g. using an enzyme-linked immunosorbent assay (ELISA) technique. There is, for example, the Organon-Teknika indirect ELISA ("Vironostika" anti-HTLV-III).
In such assays, test wells in a plastics test plate are coated with the purified or partially purified virus, and samples to be tested are then added to the wells. Any antibody to LAV or another microorganism such as ATLV/HTLV will bind to the virus, and the presence of bound antibody is then determined by adding a second labelled antibody which selectively binds to the first antibody. The antibody label is then detected in suitable manner, e.g. by adding a substrate which changes color in the presence of an enzyme label. The color change is indicative of the presence of the antibody in the sample.
The restricted mode of transmission of the AIDS virus should enable effective screening of carriers, to check the spread of the virus in a population. However, the known tests are found not to be completely reliable; they tend to give an unacceptably high rate of false positive, and also negative, results. One possible reason for inaccuracy is impurity of the virus and contamination with other antigens with which antibodies in the sample will bind. Unspecific "stickiness" of the plastics material of the test plate may also cause unwanted binding of reagents.
Popovic et al, Science 224 (4 May 1984) 497-500 (and also Example 3 of U.S. Pat. No. 4,520,113), describe the detection of viruses in patients with AIDS, by the following test: cells were infected with HTLV-III and spotted on slides, human serum was added to the slides, the slides were washed and then reacted with fluorescein-conjugated goat anti-human IgG before being rewashed and examined for fluorescence under a microscope. In a control, uninfected cells were used.
Karpas, Mol. Biol. Med. 1 (1983) 457-459, had previously disclosed screening, by immunofluorescence, for the presence of antibodies in the sera of homosexuals with or without AIDS, using acetone-fixed cells. The important conclusion of Karpas's disclosure was that the sera did not have antibodies to ALV (HTLV), and that another virus might be involved in the development of AIDS.
It would be very desirable to provide a cheaper and more convenient test for AIDS than immunofluorescence, while minimizing or avoiding the occurrence of false positive reactions.